Getting out of Auto: Understanding Aperture
If you want to get creative with your photography, and out of that all-too-tempting automatic mode, you'll need to get your head around a few key settings. We've already looked at ISO, and now it's the turn of aperture. Here we explain what aperture is, how it works, and what impact changing it will have on your photographs.
What is aperture?
In simple terms, aperture refers to the opening of a lens diaphragm through which light passes. Changing this setting – which is normally done via a rear or top dial, but could be accessed via buttons, or even a ring on the lens – lets you adjust the size of this hole, with diaphragm blades moving to control how much light can reach the image sensor (or film).
Different aperture values are described in f-numbers, and are calculated using the lens focal length to the aperture diameter. However, you don't really need to understand how it is calculated, but just that larger f-numbers refer to smaller holes, which means less light gets through and results in darker photos.
Each full f-stop jump (F1.4, F2, F2.8, F4, F5.6, F8, and so on), sees the aperture halve, and therefore half the amount of light passes through. This is why lenses with wider maximum apertures – think F1.4 and F1.8 optics – are prized by snappers and often seen as preferable in low light situations (where using a slower shutter speed to get extra light won't cut it) as they can physically let more light in. As such, maximum aperture is one of the most important things to consider when choosing a new lens.
What else do different apertures do?
Having a grasp of what aperture physically is, and how f-stop numbers work, puts you well on the way to understanding aperture, but it's also vital to know what impact changing the setting will have on your photos, beyond the amount of light being allowed through. Wider apertures (remember that's the smaller f-numbers) result in a shallower depth of field, the part of your image which is in focus.
This means wider apertures can be used to make a subject pop from a blurred background. Equally, narrower apertures (bigger f-numbers) can be used to keep subjects in focus, even if they are at different distances from your lens. This can be seen in the series of images above, where at F1.8 only the coffee is in focus, but as the aperture narrows, objects in front and behind also come into focus. Obviously shutter speeds were adjusted here to keep a consistent exposure as just changing aperture would have also meant images got darker as the aperture narrowed.
It's worth noting that distance from lens also impacts the depth of field, so while shooting at F1.8 up close might give you just a couple of centimeters of focus, using the same lens and settings to shoot a subject further away will give a wider depth of field.
How to use different apertures
Unfortunately, as with many photographic settings, using aperture is a case of give and take. Because changing aperture is going to impact both depth of field and the amount of light in an image, you'll need to balance changes with adjustments to ISO and shutter speed to create the exposure you are going for.
This means you can't just change aperture to increase the depth of field in a shot, as it will also make your image darker. As such, you will also need to balance shutter speed or ISO depending on what you are shooting. Equally you can't always select a wider aperture if you are struggling for light, as it will also narrow your depth of field, which might mean important parts of your shot are no longer in focus.
We'd advise those who are just getting to grips with the setting to begin by experimenting with the Aperture Priority mode on their camera. This lets you take control of depth of field by adjusting the aperture, while the camera automatically balances shutter speed and (if also using auto ISO) ISO sensitivity.
Once you are confident about how adjusting aperture will change your images in terms of depth of field, you can then move on to full manual settings. This will mean you get to choose aperture, shutter speed and ISO settings to create the images you want to capture, which might not have been possible in automatic modes.
Understanding aperture numbers on lenses
All of those numbers on the barrel and face of a lens can be daunting, but they can also tell you a lot about the optic, and whether it's going to let you take the sort of photos you want. One number that almost all lenses will display is a maximum aperture, that's the widest aperture available. It'll probably be displayed like 1:1.8 (meaning a F1.8 maximum aperture).
However, unlike smartphones with their typically fixed aperture lenses, it's important to note that you are not limited to shooting at this maximum aperture. Just because you have a F1.8 lens doesn't mean you have to shoot everything at F1.8, you can dial that aperture narrower.
If your lens has a maximum aperture range, that means it has a variable aperture, and the maximum aperture you can select will change depending on the focal length of the lens. For example, if it says 1:2.8-5.6, it will let you shoot at F2.8 at its widest focal length, but only offer a maximum of F5.6 at full zoom.
It's also worth noting that variable maximum apertures are not always a smooth sliding scale. For example an 18-200-mm F3.5-F6.5 lens might reach its maximum F6.5 aperture limit from 120-mm onward.
Examples of photos using wide apertures
Here are some examples of images shot with wider apertures. As you can see there are many situations in which you might want to shoot with a wide aperture. It might be because you want a shallow depth of field to make a subject pop, or to isolate a portrait subject from a blurred background. It could be that a wide aperture is needed to shoot in a low light situation while retaining the shutter speed and ISO setting you wanted.
Examples of photos using narrow apertures
Times when you're likely to find yourself wanting to shoot with a narrow aperture are when you want a wider depth of field, maybe to capture a group shot or a subject along with their environment. Narrow aperture settings also allow you to shoot with slower shutter speeds, which can be useful if you are getting creative with motion-blur or light trails.
We hope this guide has given you a basic understanding of what aperture is and how it can impact your photography. Controlling both light and depth of field, it's a setting which, once mastered, will really allow you to get creative and start taking photos which automatic modes just don't.
As we said earlier, the aperture priority mode on your camera is a good place to start playing around with the setting, and the joy of shooting digital is that you can take as many shots as you want. Why not try adjusting the aperture between a series of shots to see for yourself what it does?
Once you've got your head around this, as well as what ISO and shutter speed (which we'll look at next) do, then you can move onto full manual settings and start shooting the images as you imagine them.
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